The present invention is directed to a link pre-establishment control mechanism (or auto-spid detector) employed by the microcontroller of integrated services digital network (ISDN) terminal equipment, for automatically determining the service profile identifier (SPID) of the telecommunications switch installed by the local service provider to couple the customer""s equipment with the network, so that the terminal equipment may gain connectivity (place a call) through the switch and over the network to a destination site. The invention is particularly directed to a mechanism for automatically determining the SPID for a subdivided area code application.
As described in the above-referenced ""519 application, integrated services digital network (ISDN) communications make it possible for telephone service providers to supply multiple types of signalling channels from a central office over a single twisted pair-configured, local loop to a network termination interface or ISDN terminal equipment. Such equipment may include, but is not limited to an ISDN phone, an X.25 packet device, or an ISDN terminal adapter, to which customer premises-resident data terminal equipment may be coupled. These multiple types of signalling channels typically include a digital data channel, a digitized voice channel and a separate dialing channel.
In order for a customer to place a call through an installed piece of terminal equipment, it is necessary that the terminal equipment""s supervisory communications controller be properly preconfigured with a prescribed set of communication parameters. These parameters include the telecommunications switch protocol employed in the local service provider""s central office facility, the local directory numbers (LDNs), including area codes, associated with the two ISDN bearer (B1, B2) channels, and a service profile identifier or SPID. The SPID is a sequence of digits, which identifies the ISDN terminal equipment that is coupled to the ISDN switch, and is assigned by the local telephone service provider, when the ISDN line is installed. The number of SPIDs required (0, 1 or 2) will depend upon how the ISDN line is configured.
Now even though the switch protocol and SPID parameters are routinely supplied by the telephone service provider to the purchaser of the ISDN terminal equipment, the end user, being technically unsophisticated, is usually accustomed to doing nothing more than simply installing an analog modem in the customer""s premises-located equipment, and plugging in a telephone connector to a modem port (RJ 11 jack). Unfortunately, experience has shown that on the order of eighty percent of ISDN customers will burden the equipment supplier and/or the local telephone service provider with requests for technical support, in the course of configuring the settings for ISDN terminal equipment, even if the service provider has correctly assigned each of the switch protocol, SPID and LDN parameters for use by the customer""s ISDN terminal equipment.
Advantageously, the invention described in the ""519 successfully remedies this problem by means of an automated SPID/switch detector mechanism (or auto-spid detector), that is incorporated into the terminal equipment""s communications control software. The only customer participation required is that of inputting the local directory numbers (including area code), and invoking the SPID/switch detection mechanism via a user interface. Once invoked, the auto-spid detector proceeds to automatically step through a prescribed SPID table search and generation routine, followed by a test call communication exchange with the telecommunications switch employed by the local service provider to couple the customer""s equipment with the network.
Now although the auto-spid detector of the ""519 application automatically generates SPIDs for a customer""s ISDN terminal equipment, it is subject to potential failure, if the area code information given by the customer is that of an area code that has been recently subdivided la or xe2x80x98splitxe2x80x99 into one or more new area codes. In such an event, since the switch is configured for accepting SPIDs using the old area code (that prior to the area code subdivision), then even if all of the steps of the auto-spid detection routine described in the ""519 application are executed correctly, and otherwise accurately identify the format and type of switch employed by the telephone service provider, entry of the new area code by the user can be expected to prevent any of the iteratively generated SPID formats from being compatible with the parameter information used by the switch, so that the auto-spid detection routine will fail.
In accordance with the present invention, this subdivided or split area code problem is successfully addressed by modifying the auto-spid generation routine of the ""519 application, in a manner that causes the routine to execute an area code change and retry procedure in the event that, after potential failure of the original auto-spid detection routine, it is determined that the area code originally entered by the user and employed by the SPID generation routine is an area code that has been derived by subdividing a previous area code (for which the switch is currently configured) into one or more new area codes.
For this purpose, should a potential failure condition be reached, then before actually declaring a failure, a subdivided, or split, area code table is searched to determine whether the originally customer-supplied area code is listed with a link to a previous area code. This link may comprise a dual listing of both the current area code and a previous area code. If the current area code is not listed, it is inferred that the area code is not a split or subdivided area code, and a failure declared. Alternatively the link may comprise a pointer to another area code.
If such a link is found, then the currently used area code is replaced with the other (previous) area code for that listing, and the auto-spid routine is rerun, in its entirety, using the replacement area code that has been subdivided into two or more area codes (one of which is the currently employed area code as supplied by the customer). During rerun of the auto-spid detection routine, using the changed (previous) area code, as during the initial processing sequence, the auto-spid detection mechanism iteratively attempts to register respectively different service profile identifiers (SPIDs), as necessary, using the replacement area code, until the correct SPID and corresponding switch protocol is identified.